The present invention relates to a device and a method for measuring the temperature of a heated metal conveyor commonly known as a laminator.
Devices for the continuous production of foam blocks having a rectangular cross-section are well known. These devices typically comprise an endless conveyor belt with sidewalls in which the carrying run of the conveyor belt and the sidewalls are adapted to be covered with a film, a distributing device for a foamable reaction mixture which is located over the inlet end of the conveyor belt and a plurality of mold covers which are placed along the foaming area and fixed to guiding mechanisms. The conveyor belt is frequently a continuous belt-type conveyor consisting of multiple strands of chain with slats of metal (generally steel or aluminum) attached across the chains thereby forming a "belt." These metal slats are commonly called platens. Such devices are described in U.S. Pat. Nos. 3,579,722; 3,528,126; 4,060,579 and 4,120,626. Typically, a foamable reaction mixture is continuously injected into the closed foaming space formed by conveyor belts, lateral side boundaries and a finished section of foam plastic.
The temperature of this closed foaming space must be carefully monitored in producing high quality polyurethane and isocyanurate foams. If the temperature is too low, the product may be undesirably soft. If the temperature is too high, the foaming reaction proceeds too quickly and voids develop in the product. Accurate temperature measurement is difficult, however, due to the movement of the conveyor platens and the likelihood that a device in contact with these platens will get caught between those platens.
One possible approach to measuring the temperature in a laminator makes use of infrared spectroscopy. However, temperatures measured by this method are only accurate to .+-.3.degree. F. Another disadvantage of this IR method is that measurement of the temperature within the central region of the laminator during the foaming operation would require opening the closed space of the laminator causing heat loss that would deleteriously affect the product foam. This potential heat loss, therefore, precludes temperature measurement by the IR method while the laminator is running. This method has the further disadvantage of being quite expensive.
Laminator temperature may also be measured by means of a pyrometer. With the exception of platinum pyrometers, however, a significant period of adjustment is required. Less expensive pyrometers (i.e., those not employing platinum) are also disadvantageous in that they are only accurate to .+-.5.degree.-10.degree. F. Pyrometers are also limited in that they can only measure the temperature at the end of the laminator because the conveyor moves too rapidly during operation of the laminator to permit accurate measurement of the temperature.
It would be advantageous, therefore, to have a device capable of accurately measuring the temperature of both the end and middle sections of a laminator during its operation, which device would not get caught between the platens of the conveyor belt and would be both durable and inexpensive .